Are there really more births on full moons?

Anecdotal Proof for the Lunar Effect

Many labor nurses will tell you that their wards fill up on full moons.
Many labor nurses will tell you that their wards fill up on full moons.
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If you ask around, you'll probably find that most people who believe in the lunar effect on birth rates rely on anecdotal proof: namely, stories related by medical professionals working in the obstetrics field. Labor nurses are often cited as providing evidence of the effect in the form of personal experience, basically relating that the number of labor-ward admissions increases on a full moon.

And who doesn't trust a labor nurse? Certainly, they're experts in the area of childbirth. But for a number of reasons that we'll get into on the next page, anecdotal evidence of this sort is notoriously unreliable.

There is, however, a limited body of more empirical evidence for the existence of the phenomenon. A 1959 study broke the month into consecutive three-day periods and found that the three days of a "full moon window" -- the day before, day of and day after a full moon -- had more births than any other single three-day period [source: Shulman]. Another study, this one published in 1966, studied birth rates by moon phase -- full, half, one-quarter and three-quarter. The authors found that within the study period, more births centered around the full-moon phase than any other [source: Shulman].

But as you get deeper into the scientific study of the connection between birth and the full moon, it quickly becomes clear that these studies supporting the lunar effect are an anomaly. The vast majority of evidence reveals the lunar effect to be myth, not scientific reality.

And sometimes, studies seem to be misread by supporters of the belief. An article on the Web site BirthSource, for instance, makes the following statement:

Talk to nurses who work labor and delivery on a regular basis […] and they will all tell you that they believe in the power of the full moon. […] Another such study seems to verify this. Examined was the relationship between lunar position and the day of delivery […] The results showed a connection between spontaneous full-term deliveries and the lunar month. [source: BirthSource]

However, if you look at the abstract for the study the text refers to, [please note, in the source list, the article cites the study as reference "5," but in fact this text refers to reference "3."] you find the following statement:

[The effect of lunar phases on the time of delivery] is too weak to allow for prediction regarding the days with the highest frequency of deliveries. [source: ScienceDirect]

So, where does that leave us?